Attenuation of antibiotic resistance genes in livestock manure through vermicomposting via Protaetia brevitarsis and its fate in a soil-vegetable system

Soil metabolic processes influenced by rice roots co-regulates the environmental evolution of antibiotic resistome

Plant root activities lead to significant differences in metabolites between the rhizosphere and non-rhizosphere soil, profoundly affecting microbial distribution. However, how this process drives the migration and propagation of manure-derived antibiotic resistance genes (ARGs) in farmland ecosystems remains unclear. Herein, we used a rice pot microcosm experiment to explore the characteristics of antibiotic resistome and bacterial communities in rhizosphere and non-rhizosphere soils and the driving effects of rhizosphere metabolites on ARG propagation. The results showed significant differences in some ARGs and bacterial diversity in rhizosphere and non-rhizosphere soils with varied differential ARGs between different growth stages of rice (P < 0.05). The biosynthesis of secondary metabolites and glutathione metabolism were found to be the main pathways affecting ARG differences in rhizosphere and non-rhizosphere soils under manure application. Structural equation modeling (SEM) analysis further indicated that ARG distribution differences between rhizosphere and non-rhizosphere soils were mainly regulated by differential metabolites, which influenced the ARG distribution by altering the succession of soil microbial communities. These results demonstrate the role of differential metabolites resulting from rice root activities in co-regulating ARG distribution, providing new insights into the regulatory mechanisms of soil ARG dynamics in paddy fields.

Are earthworms the victim, facilitator or antidote of antibiotics and antibiotic resistance at the soil-animal-human interface? A One-Health perspective

The transfer of antibiotics and antibiotic resistance (AR) to the soil systems poses ecological hazards to various organisms, including earthworms. Understanding the complex interactions between earthworms, antibiotics, and AR in the soil system requires a comprehensive assessment. Hence, the present review investigates the behaviour, fate, impacts, and mechanisms involved in the interaction of earthworms with antibiotics and AR. The antibiotics and AR detected in earthworms and their associated media, such as vermicompost, are presented, but several other antibiotics and AR widely detected in soils remain understudied. As receptors and bioassay organisms, earthworms are adversely affected by antibiotics and AR causing (1) acute and chronic toxicity, and (2) emergence of AR in previously susceptible earthworm gut microbiota, respectively. The paper also highlights that, apart from this toxicity, earthworms can also mitigate against antibiotics, antibiotic-resistant bacteria and antibiotic-resistance genes by reducing bacterial diversity and abundance. The behaviour and fate processes, including biodegradation pathways, biomarkers of antibiotics and AR in earthworms, are discussed. In addition, the factors controlling the behaviour and fate of antibiotics and AR and their interactions with earthworms are discussed. Overall, earthworms mitigate antibiotics and AR via various proximal and distal mechanisms, while dual but contradictory functions (i.e., mitigatory and facilitatory) were reported for AR. We recommend that future research based on the One-World-One-Health approach should address the following gaps: (1) under-studied antibiotics and AR, (2) degradation mechanisms and pathways of antibiotics, (3) effects of environmentally relevant mixtures of antibiotics, (4) bio-augmentation in earthworm-based bioremediation of antibiotics, (5) long-term fate of antibiotics and their metabolites, (6) bio-transfers of antibiotics and AR by earthworms, (7) development of earthworm biomarkers for antibiotics and AR, (8) application of earthworm-based bioremediation of antibiotics and AR, (9) cascading ecological impacts of antibiotics and AR on earthworms, and (10) pilot-scale field applications of earthworm-based bioremediation systems.

Effects of earthworms on antibiotic resistance genes in different soil-plant systems

Earthworms play an important role in the soil environment. To explore the difference in earthworms influence on various media in different soil-plant systems, the abundance of tetracycline, sulfonamide and quinolone resistance genes and the structure of the bacterial community were analysed from five different media including non-rhizosphere soil, rhizosphere soil, phyllosphere, root endophytes and earthworm intestine by real-time quantitative PCR and high-throughput 16S rRNA sequencing. Studies have shown that earthworms can reduce the absolute abundance of antibiotic resistance genes (ARGs) in non-rhizosphere soil. Root endophytes in the soil-cabbage system and rhizosphere soil in the soil-setaria system had the same findings. Earthworms can change the bacterial community structure, especially that of Proteobacteria and Cyanobacteria in the phyllosphere and root endophytes. Redundancy analysis (RDA) results that bacterial community change was the main factor affecting ARGs. In addition, earthworms increased the proportion of Cyanobacteria in root endophytes, and Cyanobacteria was significantly positively correlated with sul3. This study provides a scientific basis for controlling the migration and diffusion of ARGs and reducing environmental risks in soil-plant systems in the future.

Waste to value: Global perspective on the impact of entomocomposting on environmental health, greenhouse gas mitigation and soil bioremediation

The innovative use of insects to recycle low-value organic waste into value-added products such as food, feed and other products with a low ecological footprint has attracted rapid attention globally. The insect frass (a combination unconsumed substrate, faeces, and exuviae) contains substantial amounts of nutrients and beneficial microbes that could utilised as fertilizer. We analyse research trends and report on the production, nutrient quality, maturity and hygiene status of insect-composted organic fertilizer (ICOF) generated from different organic wastes, and their influence on soil fertility, pest and pathogen suppression, and crop productivity. Lastly, we discuss the impact of entomocomposting on greenhouse gas mitigation and provide critical analysis on the regulatory aspects of entomocomposting, and utilization and commercialisation ICOF products. This information should be critical to inform research and policy decisions aimed at developing and promoting appropriate standards and guidelines for quality production, sustainable utilization, and successful integration of entomocompost into existing fertilizer supply chains and cropping systems.

Different ratios of Canna indica and maize-vermicompost as biofertilizers to improve soil fertility and plant growth: A case study from southwest China

Vermicomposting is recommended as an eco-friendly technology for an organic amendment to avoid the excessive use of inorganic fertilizers, which are causing environmental pollution. Here, this study evaluated soil fertility and plant growth after vermicompost amendment using reclaimed wetland plants and manure. A pot experiment was conducted to assess the seven treatments for nutrient recovery and plant growth: a control group without any fertilization (CK); four groups with vermicompost prepared from different ratios of ecological wetland plant residues, maize, and pig manure (V1, 4:6; V2, 5:5; V3, 6:6; and V4, 7:3); one group with only Canna indica (V5, Ci), and a group with synthetic fertilizers (NPK). The results showed the remarkable impacts of Ci-vermicompost and different ratios of organic fertilizer on soil fertility and plant height (28.8%) as major outcomes. In addition, vermicompost substantially increased soil total nitrogen (60.5%), soil organic matter (60.9%) including dissolved organic carbon (52.2%), and shoot biomass (V4, three-fold increase) compared with NPK and CK. Overall, the findings of this study suggest that vermicomposting combined with wetland plants is a feasible method for organic amendments and offers an innovative approach for recycling ecological waste to produce nutrient-rich organic fertilizers, reduce environmental damage, and improve crop production.

Transformation Capability Optimization and Product Application Potential of Proteatia brevitarsis (Coleoptera: Cetoniidae) Larvae on Cotton Stalks

Cotton stalks (CS) are a potential agricultural biomass resource. We investigated the use of CS as a feed for Proteatia brevitarsis Lewis larvae and the resulting frass (larvae dung-sand) as a fertilizer. Based on a three-factor experiment (decomposition inoculant, fermentation duration, and cattle manure ratio), the optimal parameters for the transformation of CS using P. brevitarsis larvae were determined as 40-50% of cattle manure, the use of VT inoculant and a fermentation duration of 25-30 days. Regarding the products of the transformation, the protein content of the larval body was as high as 52.49%, and the fat content was 11.7%, which is a suitable-quality insect protein source. The organic matter content of larvae dung-sand was 54.8%, and the content of total nitrogen, phosphorus, and potassium (TNPK) was 9.04%, which is twice more than that of the organic fertilizer standard (NY525-2021, Beijing, China, TNPK ≥ 4.0%), and larvae dung-sand has the potential of fertilizer application. Therefore, CS as a feed and fertilizer based on the transformation of P. brevitarsis larvae is feasible, and it is a highly efficient way to promote the utilization of both CS and cattle manure.

Alteration of Manure Antibiotic Resistance Genes via Soil Fauna Is Associated with the Intestinal Microbiome

Livestock wastes contain high levels of antibiotic resistance genes (ARGs) and a variety of human-related pathogens. Bioconversion of livestock manure using larvae of the beetle Protaetia brevitarsis is an effective technique for waste reduction and value creation; however, the fate of manure ARGs during gut passage and interaction with the gut microbiome of P. brevitarsis remains unclear. To investigate this, we fed P. brevitarsis with dry chicken manure for 6 days and measured bacterial community dynamics and ARG abundance and diversity along the P. brevitarsis gut tract using high-throughput quantitative PCR and metagenomics approaches. The diversity of ARGs was significantly lower in larval midgut, hindgut, and frass than in raw chicken manure, and around 80% of pathogenicity-related genes (PRGs) exhibited reduced abundance. Network analysis demonstrated that Bacteroidetes and Firmicutes were the key bacterial phyla associated with ARG reduction. Metagenomic analysis further indicated that ARGs, mobile genetic elements (MGEs), and PRGs were simultaneously attenuated in the hindgut, implicating a decreased likelihood for horizontal gene transfer (HGT) of ARGs among bacteria and pathogens during manure bioconversion. Our findings demonstrated that the attenuation of ARGs is strongly associated with the variation of the gut microbiome of P. brevitarsis, providing insights into mechanisms of risk mitigation of ARG dissemination during manure bioconversion. IMPORTANCE Saprophagous fauna like the oriental edible beetle (P. brevitarsis) plays a fundamental role in converting organic wastes into biofertilizer. Accumulating evidence has shown that soil fauna can reduce the abundance of ARGs, although the underlying mechanism of ARG reduction is still unclear. In our previous research, we found a large reduction of ARGs in vegetable roots and leaves from frass compared with raw manure, providing a promising biofertilizer for soil-vegetable systems. Therefore, in this study, temporal dynamic changes in the microbiomes of the donor (chicken manure) and host (P. brevitarsis) were investigated, and we found a close association between the gut microbiome and the alteration of ARGs. These results shed new light on how the insect gut microbiome can mitigate manure-borne ARGs and provide insights into the bioconversion process via a typical member of the saprophagous fauna, P. brevitarsis.

Characterization of Microorganisms from Protaetia brevitarsis Larva Frass

Decomposers play an important role in the biogeochemical cycle. Protaetia brevitarsis larvae (PBLs) can transform wastes into frass rich in humic acid (HA) and microorganisms, which may increase the disease resistance of plants and promote plant growth. Beyond HA, the microorganisms may also contribute to the biostimulant activity. To address this hypothesis, we investigated the potential microbial community in the PBL frass samples and elucidated their functions of disease resistance and plant growth promotion. High-throughput sequencing analysis of four PBL-relevant samples showed that their frass can influence the microbial community of the surrounding environment. Further analysis showed that there were many microorganisms beneficial to agriculture, such as Bacillus. Therefore, culturable Bacillus microbes were isolated from frass, and 16S rDNA gene analysis showed that Bacillus subtilis was the dominant species. In addition, some Bacillus microorganisms isolated from the PBL frass had antibacterial activities against pathogenic fungi. The plant growth promotion pot experiment also proved that some strains promote plant growth. In conclusion, this study demonstrated that the microorganisms in the PBL frass are conducive to colonizing the surrounding organic matrix, which will help beneficial microbes to increase the disease resistance of plants and promote plant growth.